diff --git a/tox.ini b/tox.ini
index bbdb6ff14..e9f4951fd 100644
--- a/tox.ini
+++ b/tox.ini
@@ -13,6 +13,7 @@ deps=
     typing
 setenv =
     SPHINX_TEST_TEMPDIR = {envdir}/testbuild
+    PYTHONDONTWRITEBYTECODE = true
 commands=
     {envpython} -Wall tests/run.py -I py35 -m '^[tT]est' {posargs}
     sphinx-build -q -W -b html -d {envtmpdir}/doctrees doc {envtmpdir}/html